In many cases, it is difficult for physically handicapped or elderly people to perform an operation which can be performed easily by a healthy person.
Until today, various action-assist devices have been developed and put in practical use for such people. The action-assist devices may include a wheelchair or a care bed on which the user rides and operates a switch to drive an actuator, such as a motor, so as to assist the insufficient power. The action-assist devices may also include a wearable device which is worn by the human being and assists power needed for operation of the device based on the wearer's intention.
What is called a wearable action-assist device that can be worn by the wearer can generate a required power at any time based on the wearer's intention and a care worker is not needed. Thus, the wearable action-assist device is very useful for rehabilitation of injured or sick people and care of physically disabled persons, elderly people, etc. and its utilization is expected to grow.
There has been proposed such a wearable action-assist device in which a myoelectricity signal accompanied with a wearer's muscular line activity is detected, and an actuator is driven based on the detection result. In this wearable action-assist device, the actuator is controlled optionally according to the wearer's intention.
See the non-patent literature 1 (Takao Nakai, Suwoong Lee, Hiroaki Kawamoto and Yoshiyuki Sankai, “Development of Power Assistive Leg for Walking Aid using EMG and Linux”, Second Asian Symposium on Industrial Automation and Robotics, BITECH, Bangkok, Thailand, May 17-18, 2001).
In the meantime there is a problem in a wearable action-assist device in that, if the timing which gives the wearer the power for assistance does not harmonize with a motion of the wearer, the wearer's action becomes awkward and a sense of incongruity is given to the wearer.
It is known that, in order to harmonize the timing of power application with the motion of the wearer, it is necessary to make the timing of power application earlier than the motion of the wearer by a minute time.
However, in the wearable action-assist device of the non-patent literature 1, the processing for causing an actuator to generate power is started after the myoelectricity signal from the wearer is detected, and there is a possibility that the timing of power application later than the motion of the wearer may give the wearer a remarkable sense of incongruity.
To avoid the problem, a conventional device is proposed in which a drive control of an actuator is carried out in the following manner. The human being's action is classified into a plurality of patterns (tasks) and each task is divided into a plurality of predetermined minimum action units (phases), and a predetermined amount of current is supplied to the actuator for every phase.
See the non-patent literature 2 (“Predictive Control Estimating Operator's Intention for Stepping-up Motion by Exo-Skeleton Type Power Assist System HAL”, Proceedings of the 2001 IEEE/RSJ and International Conference on Intelligent Robots and Systems, Maui, Hi., Oct. 29-Nov. 3, 2001, pp. 1578-1583), and the non-patent literature 3 (Hideo Lee and Yoshiyuki Sankai, “Power Assist Control of Walking Aid by HAL Based on Phase Sequence and EMG”, the collection (2001) of academic lecture meeting drafts of the 19th Robotics Society of Japan).
In the wearable action-assist devices of the non-patent literatures 2 and 3, a phase of a wearer's task is estimated based on a physical quantity, such as a joint angle, which is detected from the wearer, and an actuator is controlled according to the estimated phase (autonomous control), in order to reduce the sense of incongruity accompanied with the delay of the timing of power application.